What’s Holding Up Multicast Streaming?
Dawn Rises on Multicast Streaming in 2004
Native multicast is rapidly being deployed in most large ISP’s and academic networks and, although streaming media isn’t the operators’ focus, multicast is already in widespread use today. Most financial transactions rely on data sent using multicasting (widely used in the financial services industry to push trading data to analysts’ desks). Multicasting is also widely used on the Internet 2 (the Abilene backbone is entirely native multicast-enabled) and is used in many enterprises for internal webcasts and also for videoconferencing.
The needs of the streaming media industry for efficient bandwidth utilization have not been neglected. In fact, they have led to the emergence of Source Specific Multicast.
Source Specific Multicasting (or SSM ) tunes PIM-SM to the needs of large scale, one-to-many webcasts. In SSM, each group is restricted to having only one source (the group + channel pair is called a "channel") and routing is always done using both the source and group address parts of the channel address. Knowledge of the source and group pair is assumed to come from "out-of-band," such as from a Web page. Compared to the previous model of Any Source Multicast (or ASM), the SSM model is substantially more robust and also much less subject to Denial of Service (DOS) attacks. Since the source address is always known, there is no need to do source discovery, making it much easier to provide multicast service across the entire Internet.
The advantages of multicast are now available to the streaming media industry if the managers and producers want them and take advantage of what is deployed today. New TV distribution systems using IP multicast are being built now - but generally focus only on the set-top box, not the user’s computer, to access and view multicasts. If the streaming media industry does not want to be excluded by the rapidly ongoing convergence of media distribution using the Internet, it needs to push service providers to allow user-controlled multicast access, and push itself to offer the content for users to view.
Perhaps, a decade after multicast was identified as a "real" solution to streaming media bandwidth consumption on IP networks, the promise can be realized.
Email Marshall Eubanks of TeleSuite Corporation at marshall.eubanks@telesuite.com.
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